Preparation method of ultrafine aramid nanofiber dispersion liquid

Abstract

The invention relates to the technical field of polymer materials, in particular to a preparation method of ultrafine aramid nanofiber dispersion liquid, which comprises the following steps: primarily crushing aramid III fibers to obtain pre-stripped fibers; placing the pre-stripped fiber in a potassium hydroxide / dimethyl sulfoxide / water system, stirring, and carrying out a deprotonation reaction to obtain an initial dispersion liquid with the aramid fiber concentration of 10-50 mg / mL; and standing the primary dispersion liquid at normal temperature, and further cracking the aramid fibers to obtain the ultrafine ANF dispersion liquid. According to the preparation method, high-yield and low-energy-consumption preparation of the ultrafine ANF is realized, the problem of rapid and high-yield preparation of the ANF with the size of less than 5 nanometers is solved, and the product has higher specific surface area and surface activity, higher mechanical property, better loading capacity and more excellent function regulation and control capacity and is suitable for industrial production. The method has wide application potential in the high-technology frontier fields such as aerospace, flexible electronics, advanced filtering, energy storage devices and intelligent composite structures.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and specifically to a method for preparing an ultrafine aramid nanofiber dispersion. Background Technology

[0002] Aramid fibers are a class of high-performance fiber materials with high strength, high modulus, and resistance to high temperatures and chemical corrosion. In recent years, with the development and application of nanotechnology, aramid nanofibers (ANFs) have gradually attracted the attention of research and industry. ANFs are ultrafine fiber materials with nanoscale diameters prepared by breaking down traditional aramid fibers or directly using certain processes. The main preparation methods include chemical exfoliation, electrospinning, mechanical abrasion, and post-treatment methods.

[0003] Currently, the fineness of most existing aramid nanofibers is concentrated between several hundred and tens of nanometers, and rapid and high-yield preparation of nanofibers with a size of less than 5 nanometers has not yet been achieved. For example, CN103802411B reported the preparation of aramid composite nanofiber membranes by electrospinning, with fiber diameters on the scale of hundreds of nanometers. CN118970372A reported the preparation of aramid nanofiber membranes by chemical exfoliation, achieving an average single nanofiber size of 8 nanometers. However, the aramid solid content was only set to approximately 2 mg / mL during preparation, and subsequent dilution was performed, thus significantly limiting yield. CN118932707A reported the preparation of aramid nanofibers using a high-speed emulsifier for dispersion to improve exfoliation efficiency, but the use of a superacid posed a greater challenge to the production environment. CN115110306B reported a ball mill-assisted ANF preparation method, which improved exfoliation efficiency, but the capacity limitation of the ball mill container prevented the rapid preparation of larger volumes of ANF dispersions. CN118531520A reported a carbon dioxide-assisted ANF preparation method, which also improved exfoliation efficiency, but the aeration operation increased the complexity of the preparation process, and the airtightness requirements placed an additional burden on stirring, without significantly improving the fineness of the ANF.

[0004] The aforementioned technical limitations restrict the industrialization process and application scope of aramid nanofibers. Therefore, it is necessary to improve existing methods for preparing aramid nanofibers. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing ultrafine aramid nanofiber dispersions. Using aramid III fibers as the main material, ANF is prepared by a combination of pulverization and stirring, achieving high-yield and low-energy-consumption preparation of ultrafine ANF and solving the problem of rapid and high-yield preparation of ANF with a size of less than 5 nanometers.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: On one hand, the present invention provides a method for preparing an ultrafine aramid nanofiber dispersion, comprising the following steps: S1. The aramid III fiber is initially crushed to obtain pre-stripped fiber; S2. Place the pre-stripped fiber in a potassium hydroxide / dimethyl sulfoxide / water system and stir to carry out a deprotonation reaction to obtain an initial dispersion with an aramid concentration of 10-50 mg / mL; S3. The initial dispersion was allowed to stand at room temperature, and the aramid fibers were further decomposed to obtain an ultrafine ANF dispersion.

[0007] In some specific embodiments, aramid III short fiber bundles are placed in a blade shredder for initial processing. Through the centrifugal force of rotation inside the shredder, the shearing force of the blade impact, and the collision and friction between fibers, the aramid III short fiber bundles are fully dispersed and broken. The shredded aramid III short fibers are added to a potassium hydroxide / dimethyl sulfoxide / water system and stirred at room temperature to uniformly disperse the aramid III short fibers in the solution and undergo preliminary deprotonation, causing the overall solution color to change from transparent to light yellow. The mixture is then allowed to stand for 24 hours, during which the aramid microfibers undergo further pyrolysis, gradually branching and peeling, and the diameter of the single fiber is reduced to the nanoscale. The solution color changes from light yellow to orange-red, thus preparing an ultrafine ANF dispersion with high solid content and an ANF diameter of 1-5 nm.

[0008] Furthermore, in S1, the aramid III fiber is in the form of one of chopped strands, filaments, precipitate, or pulp.

[0009] In some preferred embodiments, the aramid III fiber is a chopped fiber.

[0010] Further, in S1, the length of the aramid III fiber is 1-40mm; or 1-30mm; or 1-20mm; or 1-10mm; or 1-8mm; or 1-5mm; or 4-7mm.

[0011] In some preferred embodiments, the aramid III fiber has a length of 1-5 mm.

[0012] Further, in S1, the crushing conditions are that the blade rotation speed is 1000-50000 r / min, or 3000-40000 r / min, or 5000-30000 r / min, or 10000-30000 r / min; or 10000-20000 r / min.

[0013] In some specific embodiments, the blade rotation speed can be selected as 1000 r / min, 2000 r / min, 3000 r / min, 4000 r / min, or 5000 r / min.

[0014] Furthermore, in S1, the pulverizing time is 30-180s, or 30-90s, or 60-120s.

[0015] In some specific embodiments, the pulverization time can be selected as 30s, 45s, 60s, 750s, 90s, 110s, 130s, 150s, or 180s.

[0016] Further, in S2, the mass-to-volume ratio of aramid, water, potassium hydroxide and dimethyl sulfoxide is (10-50) g: (1-80) g: (1-40) g: (900-1100) mL.

[0017] In some specific embodiments, the mass-to-volume ratio of aramid, water, potassium hydroxide and dimethyl sulfoxide is (10-40) g: (20-80) g: (10-40) g: (900-1100) mL; or, the mass-to-volume ratio of aramid, water, potassium hydroxide and dimethyl sulfoxide is (20-40) g: (40-80) g: (20-40) g: (900-1100) mL.

[0018] Further, in step S2, the stirring conditions are a stirring speed of 50-500 r / min or 100-400 r / min. Or 100-300 r / min, or 150-300 r / min, or 200-250 r / min.

[0019] In some specific embodiments, the stirring speed can be selected as 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, or 500 r / min.

[0020] Furthermore, in S2, the stirring time is 10-60 min, or 10-45 min, or 20-40 min, or 30-40 min.

[0021] In some specific embodiments, the stirring time can be selected as 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min.

[0022] Furthermore, in S3, the settling time is 12-72h, or 24-72h, or 48-72h.

[0023] In some specific embodiments, the settling time can be selected as 12h, 18h, 24h, 30h, 36h, 42h, 48h, 54h, 60h, 66h, or 72h.

[0024] Furthermore, the diameter of the aramid nanofibers in the ultrafine ANF dispersion in S3 is 1-5 nm.

[0025] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the inherent brittleness of aramid III fiber to perform initial peeling and cracking of the fiber raw material, thereby increasing the contact area between the fiber raw material and the alkaline solution and accelerating the dispersion time. Then, a simple deprotonation operation is carried out using a potassium hydroxide / dimethyl sulfoxide / water system. Only a very short time and low-speed stirring are required, followed by standing for tens of hours to form uniform and ultrafine nanofibers. This invention is simple to process, has low equipment requirements, does not require long-term high-speed stirring, the stirring time is less than 1 hour, the total preparation time is 24-48 hours, the energy consumption is greatly reduced, and the obtained ANF dispersion has a high aramid solid content of 10-50 mg / mL, while the diameter of ANF in the dispersion is <5 nm, which balances yield and fineness.

[0026] (3) The ultrafine ANF dispersion prepared by the present invention has higher specific surface area and surface activity, higher mechanical properties and better loading capacity and better functional regulation capability, and has broad application potential in high-tech frontier fields such as aerospace, flexible electronics, advanced filtration, energy storage devices, and intelligent composite structures. Attached Figure Description

[0027] Figure 1 This is an optical microscope image of aramid III fibers according to an embodiment of the present invention. 1a is an optical microscope image of aramid III chopped fibers before pulverization; 1b is an optical microscope image of aramid III chopped fibers after pulverization. Figure 2 This is a scanning electron microscope image of aramid III fiber according to an embodiment of the present invention; 2a is a SEM image of the surface morphology of aramid III chopped fibers before pulverization; 2b is a SEM image of the surface morphology of aramid III chopped fibers after pulverization. Figure 3 This is an atomic force microscope image of an ANF dispersion according to an embodiment of the present invention; 3a is an atomic force microscope image of aramid III nanofibers; 3b is an ANF height curve. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the test materials used in the following embodiments were purchased from conventional biochemical reagent stores. Unless otherwise stated, percentages and parts are by weight. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar with the art. Furthermore, any methods and materials similar to or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0029] The endpoints of the ranges and any values ​​disclosed herein are not limited to that precise range or value. A range or value should be understood as including values ​​that are close to these ranges or values. For numerical ranges, each range... Between the endpoint values ​​of the range, between the endpoint values ​​of each range and individual point values, and between individual point values. They can be combined to obtain one or more new numerical ranges, which should be considered as being within the scope of this paper. The specific details will be disclosed in the official publication.

[0030] Based on this invention, heterocyclic aramid fibers possess superior mechanical strength, modulus, electrical insulation, corrosion resistance, and high-temperature resistance. They are primarily obtained through the copolymerization of three monomers: p-phenylenediamine, terephthaloyl chloride, and a diamine containing heterocyclic structures with elements such as N, O, and S, and are also known as aramid III fibers. Compared to aramid II fibers, aramid III fibers are more prone to core-sheath separation during friction, leading to fibrillation and fiber splitting. Simultaneously, the newly introduced benzimidazole heterocycles on aramid III fibers provide more polar and reactive sites, which can introduce additional negative charges during deprotonation, significantly enhancing the electrostatic repulsion between ANFs, thus facilitating dissociation to obtain smaller diameter and more uniformly distributed ANFs.

[0031] Chemical exfoliation is based on the deprotonation of amide bonds within aramid fibers by a strong alkali system, achieving nanoscale exfoliation of the fibers. Since fibrillation of aramid fibers mainly occurs at the ends rather than in the middle, shorter nanometer-sized aramid fibers are more easily subjected to rapid chemical exfoliation.

[0032] This invention uses aramid III fiber as the main material. First, the fiber raw material is initially peeled and cracked. Then, a simple deprotonation operation is carried out using a potassium hydroxide / dimethyl sulfoxide / water system. Only a very short time and low-speed stirring are required to achieve rapid chemical peeling of the fiber raw material in an alkaline solution. After standing for tens of hours, a uniform ANF dispersion with a size of less than 5 nanometers can be formed.

[0033] Based on this invention, ultrafine ANF possesses high specific surface area and surface activity, and the significantly reduced fiber diameter greatly increases the surface area per unit mass of fiber. This facilitates more thorough contact with matrix materials, functional components, surfactants, and even gas and liquid molecules, improving the interfacial adhesion, filtration efficiency, and effectiveness of composites with other functional nanoparticles.

[0034] Based on this invention, ultrafine ANF exhibits higher mechanical properties and better load-bearing capacity. The smaller the diameter of the nanofibers, the more ordered the molecular orientation and chain segment arrangement within the fiber material, resulting in a relatively low defect density. This allows individual fibers to achieve higher tensile strength and modulus. Simultaneously, finer fibers can be more uniformly dispersed in the composite material, facilitating uniform stress transfer and improving the overall mechanical properties and toughness of the composite material.

[0035] Based on this invention, ultrafine ANFs exhibit superior functional control capabilities. The nanoscale provides greater flexibility for functionalization and surface modification. By modifying the surface of nanoscale fibers with functional molecules and nanoparticles (such as carbon nanotubes, graphene, and metal nanoparticles), the electrical conductivity, thermal conductivity, electromagnetic shielding ability, surface hydrophilic / hydrophobic properties, and adsorption capacity of the fibers can be precisely controlled.

[0036] Based on this invention, ultrafine aramid nanofibers exhibit better processability and composite properties. Smaller aramid nanofibers can form stable dispersions in various media (such as aqueous or organic phases), facilitating their composite formation with polymers, resins, metal matrices, and even ceramic materials to prepare multifunctional, high-performance, and lightweight composite structural components.

[0037] Based on this invention, the ultrafine ANF obtained can help its macroscopic products achieve more groundbreaking applications in high-tech frontier fields such as aerospace, flexible electronics, advanced filtration, energy storage devices, and intelligent composite structures.

[0038] Based on the present invention, the ultrafine aramid nanofiber dispersion is prepared by the following steps: Aramid III fibers were initially pulverized to obtain pre-stripped fibers. The pre-stripped fibers were placed in a potassium hydroxide / dimethyl sulfoxide / water system and stirred to carry out a deprotonation reaction, resulting in a preliminary dispersion with an aramid concentration of 10-50 mg / mL. The preliminary dispersion was allowed to stand at room temperature, and the aramid fibers were further pyrolyzed to obtain an ultrafine ANF dispersion.

[0039] Based on the present invention, the aramid III fiber is in the form of one of chopped strands, filaments, precipitates, or pulp.

[0040] In some preferred embodiments, the aramid III fiber is a chopped fiber.

[0041] Based on the present invention, the length of the aramid III fiber is 1-40 mm; or 1-30 mm; or 1-20 mm; or 1-10 mm; or 1-8 mm; or 1-5 mm; or 4-7 mm; in some preferred embodiments, the length of the aramid III fiber is 1-5 mm.

[0042] Based on this invention, the pulverizing conditions are a blade rotation speed of 1000-50000 r / min, or 3000-40000 r / min, or 5000-30000 r / min, or 10000-30000 r / min; or 10000-20000 r / min. In some specific embodiments, the blade rotation speed can be selected as 1000 r / min, 2000 r / min, 3000 r / min, 4000 r / min, or 5000 r / min.

[0043] Based on this invention, the pulverization time is 30-180s, 30-90s, or 60-120s. In some specific embodiments, the pulverization time can be selected as 30s, 60s, 90s, 120s, or 180s.

[0044] Based on the present invention, the mass-to-volume ratio of aramid, water, potassium hydroxide and dimethyl sulfoxide is (10-50) g: (1-80) g: (1-40) g: (900-1100) mL; in some specific embodiments, the mass-to-volume ratio of aramid, water, potassium hydroxide and dimethyl sulfoxide is (10-40) g: (20-80) g: (10-40) g: (900-1100) mL; or, the mass-to-volume ratio of aramid, water, potassium hydroxide and dimethyl sulfoxide is (20-40) g: (40-80) g: (20-40) g: (900-1100) mL.

[0045] Based on the present invention, the stirring conditions are a stirring speed of 50-500 r / min, or 100-400 r / min, or 100-300 r / min, or 150-300 r / min, or 200-250 r / min; in some specific embodiments, the stirring speed can be selected as 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, or 500 r / min.

[0046] Based on the present invention, the stirring time is 10-60 min, or 10-45 min, or 20-40 min, or 30-40 min; In some specific embodiments, the stirring time can be selected as 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min.

[0047] Based on this invention, the settling time is 12-72h, or 24-72h, or 48-72h; in some specific implementations, the settling time can be selected as 12h, 18h, 24h, 30h, 36h, 42h, 48h, 54h, 60h, 66h, or 72h.

[0048] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying tables. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention. Example 1

[0049] Pre-cleaned 2mm aramid III chopped fibers were placed in a blade shredder at a speed of 5000 r / min for 60 s to fully disperse and break the fiber bundles, resulting in flocculent pre-stripped fibers. In a standard experimental environment (23±2℃, relative humidity 50%±10%), 10g of potassium hydroxide and 20g of deionized water were mixed to prepare a potassium hydroxide / dimethyl sulfoxide / water system, which was then added to 1000mL of DMSO. 10g of the pre-stripped fibers were then added to the system. In a potassium chloride / dimethyl sulfoxide / water system, the mixture was stirred at a constant speed of 200 r / min for 0.5 h to uniformly disperse the pre-stripped fibers in the solution and induce initial deprotonation. The overall solution color changed from transparent to light yellow, yielding an initial dispersion. The initial dispersion was then allowed to stand for 24 h. During this period, the aramid microfibers underwent further cleavage, gradually branching and peeling, reducing the diameter of individual fibers to the nanoscale. The solution color changed from light yellow to orange-red, and no obvious large solid particles were observed. An ANF dispersion with an aramid content of 10 mg / mL was obtained. Example 2

[0050] Pre-cleaned 2mm aramid III chopped fibers were placed in a blade shredder at a speed of 10000 r / min for 60 s to fully disperse and break the fiber bundles, resulting in flocculent pre-stripped fibers. In a standard experimental environment (23±2℃, relative humidity 50%±10%), 20g of potassium hydroxide and 20g of deionized water were mixed to prepare a potassium hydroxide aqueous solution, which was then poured into 1000mL of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. 20g of pre-stripped fibers were then added to a solution of hydroxide... In a potassium chloride / dimethyl sulfoxide / water system, the mixture was stirred at a constant speed of 200 r / min for 0.5 h to uniformly disperse the pre-stripped fibers in the solution and induce initial deprotonation. The overall solution color changed from transparent to light yellow, yielding an initial dispersion. The initial dispersion was then allowed to stand for 24 h. During this period, the aramid microfibers underwent further cleavage, gradually branching and peeling, reducing the diameter of individual fibers to the nanoscale. The solution color changed from light yellow to orange-red, and no obvious large solid particles were observed. An ANF dispersion with an aramid content of 20 mg / mL was obtained. Example 3

[0051] Pre-cleaned 2mm aramid III chopped fibers were placed in a blade shredder at a speed of 10000 r / min for 90 s to fully disperse and break the fiber bundles, resulting in flocculent pre-stripped fibers. In a standard experimental environment (23±2℃, relative humidity 50%±10%), 20g of potassium hydroxide and 20g of deionized water were mixed to prepare a potassium hydroxide aqueous solution, which was then poured into 1000mL of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. 20g of pre-stripped fibers were then added to a solution of hydroxide... In a potassium chloride / dimethyl sulfoxide / water system, the mixture was stirred at a constant speed of 300 r / min for 0.75 h to uniformly disperse the pre-stripped fibers in the solution and induce initial deprotonation. The overall solution color changed from transparent to light yellow, yielding an initial dispersion. The initial dispersion was then allowed to stand for 36 h. During this period, the aramid microfibers underwent further cleavage, gradually branching and peeling, reducing the diameter of individual fibers to the nanoscale. The solution color changed from light yellow to orange-red, and no obvious large solid particles were observed. An ANF dispersion with an aramid content of 20 mg / mL was obtained. Example 4

[0052] Pre-cleaned 2mm aramid III chopped fibers were placed in a blade shredder at a speed of 20000 r / min for 60 s to fully disperse and break the fiber bundles, resulting in flocculent pre-stripped fibers. In a standard experimental environment (23±2℃, relative humidity 50%±10%), 30g of potassium hydroxide and 30g of deionized water were mixed to prepare a potassium hydroxide aqueous solution, which was then poured into 1000mL of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. 30g of the pre-stripped fibers were then added to a solution of hydroxide... In a potassium chloride / dimethyl sulfoxide / water system, the mixture was stirred at a constant speed of 300 r / min for 0.75 h to uniformly disperse the pre-stripped fibers in the solution and induce initial deprotonation. The overall solution color changed from transparent to light yellow, yielding an initial dispersion. The initial dispersion was then allowed to stand for 24 h. During this period, the aramid microfibers underwent further cleavage, gradually branching and peeling, reducing the diameter of individual fibers to the nanoscale. The solution color changed from light yellow to orange-red, and no obvious large solid particles were observed. An ANF dispersion with an aramid content of 30 mg / mL was obtained. Example 5

[0053] Pre-cleaned 2mm aramid III chopped fibers were placed in a blade shredder at a speed of 30,000 r / min for 60 s to fully disperse and break the fiber bundles, resulting in flocculent pre-stripped fibers. In a standard experimental environment (23±2℃, relative humidity 50%±10%), 40g of potassium hydroxide and 40g of deionized water were mixed to prepare a potassium hydroxide aqueous solution, which was then poured into 1000mL of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. 40g of the pre-stripped fibers were then added to a solution of hydroxide... In a potassium chloride / dimethyl sulfoxide / water system, the mixture was stirred at a constant speed of 300 r / min for 0.75 h to uniformly disperse the pre-stripped fibers in the solution and induce initial deprotonation. The overall solution color changed from transparent to light yellow, yielding an initial dispersion. The initial dispersion was then allowed to stand for 24 h. During this period, the aramid microfibers underwent further cleavage, gradually branching and peeling, reducing the diameter of individual fibers to the nanoscale. The solution color changed from light yellow to orange-red, and no obvious large solid particles were observed. An ANF dispersion with an aramid content of 40 mg / mL was obtained.

[0054] Figure 1a-1b are optical microscope images of aramid III chopped fibers and pre-stripped fibers, respectively. It can be seen that after the pulverization process, the aramid III chopped fibers are not pulverized into powder particles like traditional materials. This is mainly due to the lightweight, high strength and high modulus characteristics of aramid III itself. At the same time, the bending and local splitting of the microfibers can also be clearly observed, and a black bending point appears every 100μm. This is because shear force and friction force are successfully introduced during the high-speed impact of the blade, and the fiber's inherent brittleness enables folding and splitting, thus providing faster solid-liquid interface contact and local splitting for subsequent DMSO alkaline solution mixing. Figure 2 a-2b are scanning electron microscope images of aramid III chopped fibers and pre-stripped fibers, respectively. It can be seen that the surface of the aramid III microfibers exhibits irregular splitting after being crushed and impacted, thus increasing the contact area for subsequent alkali wetting. Figure 2 This is an atomic force microscope image of the ANF dispersion; it allows for a direct view of the obtained ultrafine ANF. Example 6

[0055] Pre-cleaned 2mm aramid III chopped fibers were placed in a blade shredder at a speed of 20000 r / min for 120 s to fully disperse and break the fiber bundles, resulting in flocculent pre-stripped fibers. In a standard experimental environment (23±2℃, relative humidity 50%±10%), 40g of potassium hydroxide and 40g of deionized water were mixed to prepare a potassium hydroxide aqueous solution, which was then poured into 1000mL of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. 40g of the pre-stripped fibers were then added to a solution of hydroxide... In a potassium chloride / dimethyl sulfoxide / water system, the mixture was stirred at a constant speed of 400 r / min for 0.75 h to uniformly disperse the pre-stripped fibers in the solution and induce initial deprotonation. The overall solution color changed from transparent to light yellow, yielding an initial dispersion. The initial dispersion was then allowed to stand for 48 h. During this period, the aramid microfibers underwent further cleavage, gradually branching and peeling, reducing the diameter of individual fibers to the nanoscale. The solution color changed from light yellow to orange-red, and no obvious large solid particles were observed. An ANF dispersion with an aramid content of 40 mg / mL was obtained.

[0056] Comparative Example 1 In a standard experimental environment (23±2℃, relative humidity 50%±10%), 40g of potassium hydroxide and 40g of deionized water were mixed to prepare a potassium hydroxide aqueous solution, which was then poured into 1000mL of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. 40g of 2mm aramid III short-cut fibers were added to the potassium hydroxide / dimethyl sulfoxide / water system and stirred at a constant speed of 400r / min for 1h to uniformly disperse the aramid fibers in the solution and cause preliminary deprotonation. The overall color of the solution changed from transparent to light yellow, and the initial dispersion was obtained. The initial dispersion was then allowed to stand for 24h to obtain an ANF dispersion with an aramid content of 40mg / mL.

[0057] Comparative Example 2 In a standard experimental environment (23±2℃, relative humidity 50%±10%), 40g of potassium hydroxide and 40g of deionized water were mixed to prepare a potassium hydroxide aqueous solution, which was then poured into 1000mL of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. 40g of 2mm aramid III short-cut fibers were added to the potassium hydroxide / dimethyl sulfoxide / water system and stirred at a constant speed of 300r / min for 0.75h to uniformly disperse the aramid fibers in the solution and cause preliminary deprotonation. The overall color of the solution changed from transparent to light yellow, resulting in a preliminary dispersion. The preliminary dispersion was then allowed to stand for 72h to obtain an ANF dispersion with an aramid content of 40mg / mL.

[0058] Comparative Example 3 Pre-cleaned 2mm aramid III chopped fibers were placed in a blade shredder at a speed of 20,000 r / min for 120 s to fully disperse and break the fiber bundles, resulting in flocculent pre-stripped fibers. In a standard experimental environment (23±2℃, relative humidity 50%±10%), 20g of potassium hydroxide and 40g of deionized water were mixed to prepare a potassium hydroxide aqueous solution, which was then poured into 1000mL of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. 40g of pre-stripped fibers were added to the potassium hydroxide / dimethyl sulfoxide / water system and stirred at a constant speed of 400 r / min for 0.75 h to uniformly disperse the pre-stripped fibers in the solution and undergo preliminary deprotonation, resulting in an ANF dispersion with an aramid content of 40 mg / mL.

[0059] Comparative Example 4 Similar to Example 2, except that aramid II chopped fibers are used instead of aramid III chopped fibers, and the settling time is extended to 72 hours.

[0060] Table 1 shows the characterization data of the aramid nanofibers obtained in the examples and comparative examples.

[0061] As can be seen from Table 1, the average diameter of the ANFs obtained in Examples 1-6 is only 1-3 nm, while the solid content of the aramid raw material can be as high as 40 mg / mL. Compared with Example 5, Comparative Examples 1-2 show that without initial crushing and extended deprotonation reaction stirring time and standing time, the average diameter of the obtained ANFs is greater than 5 nm. Compared with Example 6, Comparative Example 3 has no standing time, only reduced alkali concentration and increased deprotonation reaction stirring time, and the average diameter of the obtained ANFs is greater than 15 nm. However, the aramid II system used in Comparative Example 4 is difficult to balance yield and fineness. When the solid content of aramid in the solution is 20 mg / mL, the diameter of the prepared ANF reaches 28.11 nm, which is much higher than the size of the ANFs obtained in this invention. If you want to obtain ANFs within the ten-nanometer scale, you need to reduce the solid content of aramid in the solution, and generally 2 mg / mL or even lower is selected.

[0062] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing an ultrafine aramid nanofiber dispersion, characterized in that, Includes the following steps: S1. The aramid III fiber is initially crushed to obtain pre-stripped fiber; S2. Place the pre-stripped fiber in a potassium hydroxide / dimethyl sulfoxide / water system and stir to carry out a deprotonation reaction to obtain an initial dispersion with an aramid concentration of 10-50 mg / mL; S3. The initial dispersion was allowed to stand at room temperature, and the aramid fibers were further decomposed to obtain an ultrafine ANF dispersion.

2. The method for preparing an ultrafine aramid nanofiber dispersion according to claim 1, characterized in that, In S1, the aramid III fiber is in one of the following forms: chopped strands, filaments, precipitate, or pulp.

3. The method for preparing an ultrafine aramid nanofiber dispersion according to claim 1 or 2, characterized in that, In S1, the length of the aramid III fiber is 1-40 mm; or 1-30 mm; or 1-20 mm; or 1-10 mm; or 1-8 mm; or 1-5 mm; or 4-7 mm.

4. The method for preparing an ultrafine aramid nanofiber dispersion according to claim 3, characterized in that, In S1, the crushing conditions are: the blade rotation speed is 1000-50000 r / min, or 3000-40000 r / min, or 5000-30000 r / min, or 10000-30000 r / min; or 10000-20000 r / min.

5. The method for preparing an ultrafine aramid nanofiber dispersion according to claim 1, 2, or 4, characterized in that, In S1, the pulverization time is 30-180s, or 30-90s, or 60-120s.

6. The method for preparing an ultrafine aramid nanofiber dispersion according to claim 1, characterized in that, In S2, the mass-to-volume ratio of aramid, water, potassium hydroxide and dimethyl sulfoxide is (10-50) g: (1-80) g: (1-40) g: (900-1100) mL.

7. The method for preparing an ultrafine aramid nanofiber dispersion according to claim 1 or 6, characterized in that, In step S2, the stirring conditions are a stirring speed of 50-500 r / min, or 100-400 r / min, or 100-300 r / min, or 150-300 r / min, or 200-250 r / min.

8. The method for preparing an ultrafine aramid nanofiber dispersion according to claim 7, characterized in that, In step S2, the stirring time is 10-60 min, or 10-45 min, or 20-40 min, or 30-40 min.

9. A method for preparing an ultrafine aramid nanofiber dispersion according to any one of claims 1, 2, 4, 6 or 8, characterized in that, In S3, the settling time is 12-72h, or 24-72h, or 48-72h.

10. The method for preparing an ultrafine aramid nanofiber dispersion according to claim 1, characterized in that, The diameter of the aramid nanofibers in the ultrafine ANF dispersion in S3 is 1-5 nm.

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